It is true that Europa's (almost near certain) subsurface ocean has the very strong potential to harbor life.

Even if it did not have life, Europa is geologically unique. Its surface is mostly water ice and is very active, showing very few craters. The composition of the different ices on its surface is unclear, particularly in the areas nearest to the more recently active ridges (somewhat inaccurately called triple bands). The Chaos regions show what look like iceburgs floating in a sea which melted, then froze again. It is now thought those Chaos regions did not have a liquid surface, but were instead a type of tectonic feature not seen on earth. There are huge ridge features called cycloids which span hundreds of kilometers, and at least one article I read speculated that when they form that the major faulting takes place over a span of hours or days (as opposed to years).

It goes on from there.

I think Europa's potential as a life bearing world is what puts it to the top of the list over other bodies like Io, but even if you take away the life element it is still a most interesting place.

I find your arguments about the nth question compelling. I wonder if a New Frontiers class mission could significantly improve our ability to target a follow on flagship mission. If not, then we'll be stuck in this "we don't know enough to optimally target a Titan flagship mission" loop forever.

Could we end up with a mission to both Europa/Jovian system and Titan out of the flagship definition process?

The possibility occurred to me as I was reading through the EuroPlanet abstracts. A bit of background. For Titan, ESA is looking at a balloon and lander, with the current emphasis apparently on a short-lived lake floater. The plan of record (to the extent there is one, but this is what's in the abstracts) is for the in situ elements to be released before the orbiter does the insertion burn. The orbiter then does 18 months of an orbital tour around Saturn before finally entering into a 1,500 km high circular orbit.

There are a lot implications to this plan. First, the lake floater needs a relay only for a few hours, which will presumably be done by the orbiter as it passes by Titan. Then the balloon is largely on its own and dependent on direct communication with Earth to send its data home except for brief periods when the orbiter flies by for the first 18 months. (Nominal lifetime of the balloon is given as "months.") Even after the orbiter is circling Titan, most of the balloon's data will have to be sent directly to Earth. The orbiter will have relay coverage only over a fairly thin strip along its orbit track. The movement of Titan around Saturn then will bring the balloon into this track just twice each 16 day orbit.

The net of all this long discussion is that the ESA elements of the Titan mission would be designed to operate without the orbiter. Given that, ESA could send the balloon and a short lived lander to Titan on a flyby carrier craft. This would be somewhat similar to the approached used for landers to Mars except that the carrier craft would need to have the ability to receive and relay the lander's data. NASA would still need to provide the RTG power source, and based on current launch policy for nuclear power sources, provide the launch.

... For Titan, ESA is looking at a balloon and lander, with the current emphasis apparently on a short-lived lake floater. The plan of record (to the extent there is one, but this is what's in the abstracts) is for the in situ elements to be released before the orbiter does the insertion burn. The orbiter then does 18 months of an orbital tour around Saturn before finally entering into a 1,500 km high circular orbit.

There are a lot implications to this plan. First, the lake floater needs a relay only for a few hours, which will presumably be done by the orbiter as it passes by Titan. Then the balloon is largely on its own and dependent on direct communication with Earth to send its data home except for brief periods when the orbiter flies by for the first 18 months. (Nominal lifetime of the balloon is given as "months.") Even after the orbiter is circling Titan, most of the balloon's data will have to be sent directly to Earth. The orbiter will have relay coverage only over a fairly thin strip along its orbit track. The movement of Titan around Saturn then will bring the balloon into this track just twice each 16 day orbit.

Can anyone spot a flaw in this argument (especially Ralph L)?

Yes.

You are substantially understating the ability of the orbiter and balloon to communicate outside close Titanflybys - for those months, the orbiter will still only be a million km or less away. So direct-to-Earth is notthe main conduit (although that helps fill in gaps when orbiter and balloon are on opposite sides of Titan)

You (and NASA and ESA) will hopefully be making your judgements on the final reports when they are complete rather than meeting abstracts, though I know that's all there is right now. I could believe there might be a presentation at the November OPAG meeting that might be the next public release of information.

I had wondered about long distance relay from the balloon to orbiter. That is one big antenna on the orbiter...

Still, if NASA decides on a Jovian mission, I'd still want ESA to select a Titan in situ mission over a Ganymede orbiter. That is, unless I have again substantially misunderstood how little data could be returned by a balloon at Titan without a relay.

Thanks for the clarification, Ralph. I was hoping it wasn't this dire, but after several OPAG presentations and abstracts ignoring the issue, I got to thinking...

Thanks for the update on when the downselection will be announced. I will try to post some summaries of the main final report for JEO on my blog (with a focus on Io science) while Van Kane will summarize the Titan Orbiter report on his blog, http://futureplanets.blogspot.com

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted.
Do not reproduce without permission. Read
here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the
individual posters and do not necessarily reflect the opinions
of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer
UnmannedSpaceflight.com moderation team is wholly independent
of The Planetary Society. The Planetary Society has no influence
over decisions made by the UnmannedSpaceflight.com moderators.

SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society
and is funded by donations from visitors and members. Help keep
this forum up and running by contributing
here.